Device for anchoring prestressing reinforcements

ABSTRACT

The anchoring device, for anchoring at least two reinforcements for prestressing a civil engineering works structure, has a block through which there pass at least two pairs of anchoring orifices arranged symmetrically on each side of a mid-plane of the block. The two orifices of each pair have axes substantially parallel to the mid-plane and are directed toward two opposite sides of the block to take, respectively, two ends of a taut reinforcement surrounding the structure. The block has a bearing zone pressed against the structure in response to the tension in the reinforcements.

BACKGROUND OF THE INVENTION

The present invention relates to anchoring devices for anchoring theends of reinforcements intended to stress a civil engineering worksstructure (reservoir, silo, pipe, etc)

It is commonplace for a civil engineering works structure to bereinforced by hoop reinforcements which may in particular consist ofprestressing strands. These reinforcements are kept taut in aconfiguration in which they surround the structure. Their tensioningtherefore generates compressive stresses in the structure, and these canimprove its behavior under load, particularly in the case of concretestructures.

A known anchoring device consists of a block intended to press at itsbase on a civil engineering works structure and provided with orificesin which the ends of a reinforcement surrounding the structure areimmobilized, for example using wedge-effect jaws arranged in opposition.

The orifices of such a block have to lie approximately in thecontinuation of the path of the reinforcement along the structure. Ifthey do not, the taut reinforcement has a zone of steep curvature at themouth of the orifice where it carries the risk of being weakened. Thisarrangement also prevents undesirable moments from being exerted on theblock as the reinforcement is tensioned.

However, the two orifices of the block which are intended to receive theopposite ends of the reinforcement cannot be coincident. For spacereasons, the orifices and the immobilizing means (jaws or the like) haveto be mutually offset.

In order to meet these two requirements, the orifices of the block aregiven curved shapes: on the two opposite sides of the block, the (entry)directions of the two orifices are aligned in such a way as to lie inthe plane of the turn described by the reinforcement around thestructure; then the orifices curve away from this plane on each side inorder to leave enough space for the tensioning and immobilizing means tobe installed.

One disadvantage of the anchoring blocks of this last type is that thecurvature of the orifices impedes the insertion of the reinforcements.These have a certain stiffness which opposes their entry into curvedorifices. In practice, recourse has to be had to ram-powered tools inorder to introduce the reinforcements into the anchoring block, and thisconsiderably complicates the fitting of the prestressing system. Inaddition, such anchoring cannot be used when it is desirable for thereinforcement to describe more than one turn between its two anchoredends.

It is a particular object of the present invention to alleviate thesedisadvantages by proposing an anchoring device which adequately meetsthe above requirements and is easier to mount on the civil engineeringworks structure.

SUMMARY OF THE INVENTION

To this end, according to the invention, an anchoring device anchoringat least two reinforcements for prestressing a civil engineering worksstructure comprises a block through which there pass at least two pairsof anchoring orifices arranged symmetrically on each side of a mid-planeof the block. The two orifices of each pair have axes roughly parallelto said mid-plane and are directed toward two opposite sides of theblock to take, respectively, two ends of a taut reinforcementsurrounding said structure. The block comprises a bearing zone pressedagainst the structure in response to the tension in the reinforcements.

The symmetric arrangement of the pairs of orifices on each side of themid-plane allows the moments exerted on the block to be balanced becauseof the tensioning of the reinforcements. As a consequence, the orificesdo not need to have significant curvature in order to allow thereinforcement ends to be immobilized. These reinforcements thereforeremain relatively easy to introduce, and this may in particular be donemanually.

In some preferred embodiments of the invention, recourse may possiblyalso be had to one and/or other of the following arrangements:

-   -   there are guide means receiving each reinforcement end in one of        the orifices from a reinforcement portion approaching the device        at an incidence inclined with respect to a reaction plane        perpendicular to the direction of reaction of the structure on        the bearing zone in response to the tension in the        reinforcements, the reinforcement portions from which the two        ends of a reinforcement are received in the orifices of a pair        having opposite inclinations with respect to the reaction plane;    -   the guide means comprise, for each reinforcement end, a        deflector member extending the bearing zone beyond the entrance        to the orifice receiving said reinforcement end;    -   the orifices of the block have axes roughly parallel to said        reaction plane;    -   the anchoring orifices of each pair are inclined with respect to        a reaction plane perpendicular to the direction of reaction of        the structure on the bearing zone in response to the tension in        the reinforcements, the inclinations of the orifices of the pair        being opposed with respect to the reaction plane;    -   the bearing zone of the block comprises at least one groove        roughly parallel to the mid-plane of the block, providing a        passage for a reinforcement portion held taut against the        structure;    -   the bearing zone comprises, for each pair of anchoring orifices,        a groove roughly parallel to the mid-plane of the block,        providing a passage for a central portion of the reinforcement        the ends of which are received in the anchoring orifices of said        pair to allow said reinforcement to stress the structure over        two turns between its anchored ends;    -   the bearing zone comprises a central groove roughly parallel to        the mid-plane of the block, providing a passage for a portion of        a reinforcement anchored by means of another device.

Another aspect of the invention is aimed at a system for prestressing acivil engineering works structure, comprising at least one anchoringdevice as defined hereinabove and at least two taut reinforcementssurrounding said structure, having ends held by said anchoring device.

In some preferred embodiments of this prestressing system, recourse maypossibly also be had to one and/or other of the following additionalarrangements:

-   -   each reinforcement comprises a metal strand part protected by a        tubular sheath made of plastic;    -   the sheath of the reinforcement is interrupted near each end        received in an orifice of the anchoring block, a sleeve being        placed around the portion of the metal strand part of the        reinforcement lying between the interruption in the sheath and        the entrance to the orifice, the sleeve being connected in a        sealed manner to the sheath of the reinforcement and to the        block, and the sleeve being filled with a protective material;    -   a cap covers the orifice of the block on the opposite side to        said sleeve, covering a cut-back end of the metal strand part of        the reinforcement, a protective material filling the space under        the cap;    -   the exterior shape of the sheath of each reinforcement has a        flat on the side applied against the civil engineering works        structure.

Another subject of the invention is a prestressing reinforcementcomprising a metal strand part protected by a tubular sheath made ofplastic, the exterior shape of the sheath having a flat running alongthe length of the reinforcement. Such a prestressing reinforcement canadvantageously be used in the aforesaid prestressing system. However, itcan be used in other configurations and with other types of anchoringdevice.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent inthe course of the following description of two embodiments which aregiven by way of nonlimiting example with reference to the attacheddrawings.

In the drawings:

FIG. 1 is a perspective view of an anchoring block that can be usedaccording to the invention;

FIG. 2 is a side elevation in section of the anchoring block depicted inFIG. 1, to which reinforcements are connected;

FIG. 3 is a view from above of the anchoring block depicted in FIG. 2;

FIG. 4 is a view in section and in elevation of a second embodiment ofthe anchoring block that can be used according to the invention;

FIG. 5 is a view in section of a prestressing reinforcement according tothe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The anchoring device depicted in FIGS. 1 to 3 comprises an anchoringblock 1, made for example of cast iron, intended to bear, via a bearingzone 2, on the external surface of a civil engineering works structure 3visible in part in FIG. 2.

In the example depicted, the bearing zone 2 has a flat overall shape,possibly with roughnesses to prevent the block from slipping over thestructure. The reaction of the structure 3 on the block 1 is exerted ina direction A perpendicular to the plane of the bearing zone. It shouldbe noted that the bearing zone 2 could have various shapes in order todefine the reaction direction A.

The anchoring block 1 has passing through it two pairs of anchoringorifices 4 intended respectively to receive the ends of two tautprestressing reinforcements 5.

Each reinforcement 5 surrounds the reinforced structure 3 which is, forexample, of circular cross section. The two orifices of thecorresponding pair of the block are arranged top-to-toe to retain thetwo ends of the reinforcement when the latter is tensioned. Because ofthis tensioning, the bearing zone 2 of the block finds itself pressedagainst the structure, with a reaction in the direction A.

In the example depicted, the reinforcements consist of strands. Afterthey have been tensioned, their ends 1 are immobilized in the anchoringorifices 4 by means of frustoconical jaws 10 engaged in correspondingfrustoconical portions of the orifices 4.

The anchoring orifices 4 are roughly straight, with axes D parallel to amid-plane P of the block (FIG. 3). To allow the reinforcement ends to beanchored using jaws 10, the two orifices of a pair have an offset dperpendicular to the mid-plane P of the block. The arrangement of thepairs of anchoring orifices 4 is symmetric with respect to the mid-planeP. Thus, the turning moment T.d exerted on the block 1 in the reactiondirection A by a reinforcement subjected to a tension T is compensatedfor by an opposite moment −T.d exerted in the direction A by the otherreinforcement, held taut in the same way.

In the embodiment set out in FIGS. 1 to 3, the axes D of the anchoringorifices 4 are inclined with respect to the reaction plane perpendicularto the direction of reaction A, that is to say parallel to the plane ofFIG. 3. The inclinations of the orifices of each pair are opposed withrespect to this reaction plane, as can be seen in particular in theperspective view that is FIG. 1. By virtue of these inclinations, eachreinforcement end 11 received in one of the orifices 4 is aligned with areinforcement portion approaching the block 1 at an angle of incidencewith a corresponding inclination (FIG. 2). They make it possible to takeaccount of the height H between the orifices 4 and the bearing zone 2while preventing the reinforcement from being stressed transversely atthe entrance to the anchoring orifice. Use can then be made ofreinforcements whose maximum permissible curvature is determined by thecurvature of the reinforced structure rather than by characteristics ofthe anchoring device.

The device depicted in FIGS. 1 to 3 also has the advantage of allowingeach reinforcement to toxin two turns around the structure 3 between itstwo anchored ends. For that, the bearing zone 2 of the block has twogrooves 13 (FIG. 1) approximately parallel to the mid-plane P andassociated respectively with the pairs of orifices 4. Each of thesegrooves 13 (FIG. 1) provides a passage for a central portion 6 of thereinforcement, the ends of which are received in the two orifices 4 ofthe associated pair (FIG. 3). In this way it is possible to contrive foreach taut reinforcement 6 to make two turns around the structure 3between its two anchoring points in orifices bypassing through a groove13.

As shown by FIG. 1, the beefing zone 2 of the anchoring block 1 may alsohave a central groove 14 running parallel to the plane P. This centralgroove 14 also provides a passage for a reinforcement portion 14Asurrounding the structure and anchored in another anchoring devicesituated at a different location.

For a given binding stress, the grooves 13, 14 make it possible tooptimize the number of anchoring means to be used. When the reinforcedstructure 3 has a cylindrical overall shape (for example a pipe) and itis desirable to adjust the density of taut turns surrounding thestructure per unit length, it is thus possible to take advantage of thepresence of the grooves 13 and/or 14:

-   -   the grooves 13 allow there to be two turns per reinforcement as        mentioned earlier;    -   the grooves 14 make it possible to arrange anchoring devices        with different angular positions along the structure. The        reinforcements surrounding the structure over just one turn can        then pass under the anchoring device of an adjacent        reinforcement. For example, the anchoring blocks may be        positioned in two rows parallel to the direction of the        structure and in positions that are diametrically opposed in the        transverse plane, the successive reinforcements being anchored        alternately to blocks of the two opposed rows, each        reinforcement passing under a block of the opposite row to the        one to which it is anchored.

In the alternative form of embodiment of the block that is depicted inFIG. 4, the axes D′ of the anchoring orifices 4′ of the block 1′ areparallel to the reaction plane, that is to say perpendicular to thedirection of reaction A defined by the geometry of the bearing zone 2′.To compensate for the angle between this direction D′ and the directionof incidence D″ of the reinforcement 5 at the approach to the anchoringblock 1′, a deflective saddle 12 is placed under the reinforcement 5against the anchoring block 1′. This saddle 12 may form an integral partof the block 1′ or constitute a separate piece. It extends the bearingzone 2′ beyond the mouth at the entrance to the orifice 4′. Its upperface has a slight curvature tailored to gradually deflect thereinforcement 5 between the directions D″ and D′. It thus prevents thereinforcement 5 from having a tendency to form a pronounced angle at theentrance to the orifice 4′.

The reinforcements 5 advantageously consist of individually sheathedstrands (FIGS. 2 and 3). The metal strand part 15 of each strand 5 isformed of seven metal wires twisted together, coated in a protectivematerial such as a wax or a grease and housed in an individual sheathmade of plastic 16.

Near the anchoring block 1, the sheath 16 is removed to bare the metalstrand part 15 which has alone to be gripped by the anchoring jaw 10. Toprotect the bared portion against corrosion, a sleeve 23 is placedaround this portion and connected in a sealed manner to the sheath 16and to the anchoring block 1 around the entrance to the orificereceiving the strand. The sealed connection of the sleeve 23 to thesheath 16 is achieved for example by means of a sticky and/orheat-shrinkable tape 25. The connection to the anchoring block 1 is, forexample, effected by engaging the end of the sleeve 23 in a housing ofsuitable shape 24 provided around the entrance to the orifice 4receiving the strand.

In the embodiment depicted in FIG. 2, a second protective envelope isplaced around the reinforcement 5. This is an outer tube 18 made ofplastic into which the individually protected strand is slipped. Asecond sleeve 19 surrounds the portion of the end of the strand thatprotrudes beyond this outer tube 18. This second sleeve 19 is connectedin a sealed manner, for example using sticky and/or heat-shrinkabletapes 22, to the tube 18 on the one hand and to the anchoring block 1 onthe other.

In order to install a prestressing strand in the system depicted inFIGS. 1 to 3, the procedure adopted may be as follows:

-   -   the individually protected strand is slipped into its protective        tube 18;    -   the two ends of its metal strand part 15 are bared;    -   the sleeves 23 are slipped around the strand portions protruding        from the tube 18, and the sleeves 19 are slipped around the tube        18;    -   the bared ends of the strand are engaged in their anchoring        orifices 4, something that can be done manually;    -   the first sleeves 23 and their sealing means 25, 26 are        positioned;    -   the second sleeves 19 along with their sealing means 22 are        positioned;    -   a curable material 21, such as a cement slurry or a resin, is        injected into the space between the protective sheath 16 of the        strand and its outer tube 18. This injection is performed        through a nozzle 20 of the sleeve 19, depicted in FIGS. 2 and 3;    -   once the curable material 21 has set, the strand is tensioned.        The tensioning may be symmetric, a ram pulling on each of the        ends of the strand protruding from the anchoring orifices 4. As        soon as tensioning is over, the anchoring jaws 10 are pushed        into their frustoconical housings. The tensioning may also be        performed from just one side, after having positioned a jaw on        the opposite end;    -   once the desired tension has been applied, the ram is removed        and the excess length of the strand beyond the jaw 10 is cut        off;    -   a sealed cap 30, for example made of plastic, is fitted behind        the block to cover the orifice 4, covering the cut-back end of        the metal strand part 15;    -   finally, a corrosion-proofing material 27 is injected into the        orifice 4 in which the taut strand part is housed. This        protective material 27, such as a wax or a grease, pervades the        space remaining inside the orifice 4 and under the cap 30, and        penetrates between the strand and the first sleeve 23. As shown        by FIGS. 2 and 3, this injection may be performed through an        opening 28 formed in the block 1, using a greasing nipple 29        which after injection is replaced by a plastic stopper.

By thus injecting a curable material 21 beforehand around the individualsheath 16 of the strand, damage to this individual sheath during thetensioning of this strand can be avoided, as explained in EuropeanPatent 0 220 113.

As an alternative, in order to limit the effect of hammering of thesheath along the line of contact between the strand and the prestressedstructure, use may be made of a strand that has a single protectivesheath made of plastic with an appropriate shape such as that depictedin FIG. 5. In this case, it is possible to dispense with the secondenvelope 18 and with the injecting of the curable material 21.

With reference to FIG. 5, the exterior shape of the sheath 16 of thisstrand 5 has a flat 31 running along the entire length of the strand. Byapplying this flat 31 against the prestressed structure 3, the contactforce resulting from the tension in the metal strand part 15 is spreadacross the width of the flat 31, thus attenuating the maximum value ofthe compressive stress to which the sheath 16 is subjected.

Such a flat 31 can be obtained by adapting the shape of the die used toextrude the plastic of the sheath 16 during the manufacture of strands.This sheath 16 is typically made of a high density polyethylene.

1. An anchoring device, at least two reinforcements, and a civilengineering works structure, in combination comprising: a block of saidanchoring device having at least two pairs of anchoring orificesarranged symmetrically on each side of a mid-plane of the block, whereinthe two orifices of each pair of anchoring orifices have axessubstantially included in different planes substantially parallel tosaid mid-plane and are directed toward two opposite sides of the block;and each of said reinforcements having first and second ends and acentral portion and surrounding said civil engineering works structureover two turns; wherein the block has a bearing zone pressed against thecivil engineering works structure in response to tension in thereinforcements, said bearing zone for each of said pairs of anchoringorifices comprising a groove substantially parallel to the mid-plane ofthe block providing a passage for said central portion of one of saidreinforcements and said first and second ends of each of saidreinforcements being received in the orifices of said respective one ofeach of said pairs of anchoring orifices to allow each of saidreinforcements to stress the civil engineering works structure over saidtwo turns between the first and second ends thereof.
 2. The combinationas claimed in claim 1, comprising guide means receiving the first andsecond ends of each of said reinforcements in the orifices of arespective one of each of said pairs of anchoring orifices from areinforcement portion approaching the anchoring device at an incidenceinclined with respect to a reaction plane perpendicular to a directionof reaction of the civil engineering works structure on the bearing zonein response to the tension in the reinforcements, the reinforcementportions, from which the first and second ends of each of saidreinforcements are received in the orifices of a respective one of saidpairs of anchoring orifices, having opposite inclinations with respectto the reaction plane.
 3. The combination as claimed in claim 2, whereinthe guide means comprise, a deflector member extending the bearing zonebeyond an entrance to a respective orifice of said orifices of each ofsaid pairs of anchoring orifices receiving one of the first and secondends of each of said reinforcements.
 4. The combination as claimed inclaim 2, wherein the orifices of each of said pairs of anchoringorifices of the block have axes substantially parallel to said reactionplane.
 5. The combination as claimed in claim 1, wherein the orifices ofeach of said pairs of anchoring orifices are inclined with respect to areaction plane perpendicular to a direction of reaction of the civilengineering works structure on the bearing zone in response to thetension in the reinforcements, the inclinations of the orifices of eachof the pairs of anchoring orifices being opposed with respect to thereaction plane.
 6. The combination as claimed in claim 1, wherein thebearing zone comprises a central groove substantially parallel to themid-plane of the block, providing a passage for a portion for arespective one of said reinforcements.
 7. The combination as claimed inclaim 1, wherein each of said reinforcements comprises a metal strandpart protected by a tubular sheath made of plastic.
 8. The combinationas claimed in claim 7, including an interruption wherein the sheath foreach of said reinforcements is interrupted near each of the first andsecond ends of each of said reinforcements received in a respective oneof the orifices of each of said pairs of anchoring orifices of theblock, a sleeve placed around a portion of the metal strand part of eachof said reinforcements between said interruption in the sheath and anentrance to a respective one of the orifices of each of the pairs ofanchoring orifices, the sleeve being connected in a sealed manner to thesheath of each of said reinforcements and to the block, and a protectivematerial filling each sleeve.
 9. The combination as claimed in claim 8,further comprising a cap covering each of the orifices of each of saidpairs of anchoring orifices of the block on a side opposite to saidsleeve, and covering a cut-back end of the metal strand part of each ofsaid reinforcements, wherein a protective material fills the space underthe cap.
 10. The combination as claimed in claim 7, wherein an exteriorshape of the sheath of each of said reinforcements has a flat on a sidethereof which is applied against the civil engineering works structure.